When he was President, Bill Clinton famously (and perhaps apocryphally) complained that getting Democrats to agree on a course of action was like herding cats, while the Republicans didn’t seem to have this problem. All political parties are large coalitions of people with varied interests and beliefs, but is it possible that ideological differences between the parties could play a decisive role here?

A new paper by researchers at New York University, in press at Psychological Science, suggests that the answer is yes. A large body of psychological research has shown that people tend to overestimate how much others share their beliefs, feelings, and practices. But this new research suggests that this is not the case for those on the left end of the political spectrum – in fact, it’s quite the opposite. Conservatives and moderates overestimated the degree to which other conservatives and moderates were like them, while liberals assumed they were more unique among party peers than they actually were. This “liberal uniqueness” perceptive bias could help to explain why it’s harder to get Democrats to fall in line than it is for Republicans.

Led by Chadly Stern, the scientists begin by contrasting the conservative Tea Party movement, which has successfully organized its own congressional caucus, with the liberal Occupy Wall Street movement, which was hobbled by its inability to reach consensus on issues both large (what’s our agenda?) and small (how should we respond to the NYPD’s request to take down signs?). While group member similarities (in goals, beliefs, preferences, and personalities) are crucial for organizational success, the authors wondered whether perceptions of in-group similarities were just as important. In other words, maybe if group members only thought they were the same, the group would function better.

In the first study, hundreds of people online answered forty questions about preferences and beliefs, half of them political (“America should strive to strengthen its military”) and half non-political (“I like poetry”). They then estimated what percentage of study participants who share their political beliefs (political in-group members) would agree with them on each item – in other words, if you’re a conservative, and you indicated that you liked poetry, you then estimated what percentage of other conservatives in the study liked poetry as well. Stern and colleagues then compared those estimateswith the actual figues to determine whether each participant overestimated their similarity to their political in-group (false consensus) or underestimated it (false uniqueness).

Conservatives overestimated how similar their preferences were to those of other conservatives (false consensus), while liberals underestimated how similar their preferences were to those of other liberals (false uniqueness). Political moderates also overestimated their similarity to other moderates, in line with previous findings that people in general overestimate how much other people share their preferences and beliefs. This was the case for both political (e.g., military spending) and non-political (e.g., poetry) preferences.

The second study replicated the design of the first, with one twist: everyone also filled out the Need for Uniqueness scale, with questions like “If I must die let it be an unusual death rather than an ordinary death in bed.” Again, conservatives and moderates overestimated how similar they were to their political in-group, while liberals underestimated their similarity to their political in-group. Further, these ideological differences were in part accounted for by people’s need for uniqueness – the more you expressed the desire to be different from those around you, the more you underestimated how similar you were. This suggests that liberals think they’re unique among liberals in part because they want to be unique.

Anyone who’s ever been part of a liberal counter-cultural clique will recognize this pressure to be unique, which can easily turn into an arms race. You’ve got a tattoo? Well, my skin is nothing but tattoos. You make artisanal pickles? Well, I make artisanal horseradish. You have a pet ferret? Well, I have a pet camel. And so on. But it’s this motivation to be unique – even among other liberals – that makes liberals alike. It’s a bit like the scene from Monty Python’s Life of Brian where a crowd of hundreds chants in unison: “Yes, we are all individuals! Yes, we are all different!”

While the findings make sense in light of ideological stereotypes like the gotta-be-different liberal hipster, or the conformist conservative soldier, they might not apply as well to contemporary American politics. These days you’re more likely to hear the “herding cats” phrase in reference to John Boehner’s attempts to reconcile the Tea Party faction with the rest of the Republicans in the House. It remains to be seen whether the conservative false consensus effect can lead to any real consensus in the GOP.

Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist and regular contributor to NewYorker.com. Gareth is also the series editor of Best American Infographics, and can be reached at garethideas AT gmail.com or Twitter @garethideas.

Scientific American is part of Springer Nature, which owns or has commercial relations with thousands of scientific publications (many of them can be found at www.springernature.com/us). Scientific American maintains a strict policy of editorial independence in reporting developments in science to our readers.